The main objective of this work is to fractionate, purify, and localize the repetitive DNA sequences of man, using the c-RNA/DNA CsC1 density gradient hybridization technique, high-resolution "relaxed" Cs2SO4-Ag plus density gradients and in situ hybridization to prophase G-banded chromosomes. During the coming year, particular attention will be given to the purification, characterization, and localization of specific native DNA components rich in intermediate repeated sequences. Work will also be initiated on the isolation, characterization, and localization of a repetitive RNA (chromosomal RNA) to open the way to better understanding of the possible regulatory functions of repeated DNA sequences.